TOKYO — The operator of the crippled nuclear power plant leaking radiation in northern Japan announced a plan Sunday that would bring the crisis under control within six to nine months and allow some evacuated residents to return to their homes.

The chairman of power plant administrator Tokyo Electric Power Co., who was hammered by questions over his management responsibility, also apologized for the crisis at the Fukushima Dai-ichi nuclear power plant and said he was considering stepping down.

"We sincerely apologize for causing troubles," Tsunehisa Katsumata. "We are doing our utmost to prevent the crisis from further worsening."

"I feel very responsible," he added.

Frustrations have been mounting over TEPCO's failure to resolve the nuclear crisis more than a month after a catastrophic earthquake and tsunami hit Japan on March 11, knocking out power and cooling systems at the Fukushima Dai-ichi complex.

The toll from Japan's triple catastrophe is rising. More than 13,000 people have been confirmed dead, and on Wednesday the government cut its outlook for the economy, in deflation for almost 15 years, for the first time in six months.

Fighting criticism
TEPCO unveiled a phased road map for ending the crisis at a news conference, including plans to cover the damaged reactor buildings to contain the radiation and eventually remove the nuclear fuel.

The plan was unveiled as Japan's prime minister also apologized for the nuclear crisis and U.S. Secretary of State Hillary Clinton visited to show American solidarity with the Japanese people.

Prime Minister Naoto Kan, fighting criticism at home over his own handling of the aftermath of the quake and tsunami, offered a commentary in the weekend edition of the International Herald Tribune that also appeared in The New York Times and the Washington Post.

"I take very seriously, and deeply regret, the nuclear accidents we have had at the Fukushima Dai-ichi plant. Bringing the situation under control at the earliest possible date is my top priority," Kan said in his commentary.

"We pledge our steadfast support for you and your future recovery. We are very confident that Japan will demonstrate the resilience that we have seen during this crisis in the months ahead," Clinton told reporters after meeting with Foreign Minister Takeaki Matsumoto.

Clinton said Matsumoto told her that Japan hoped for U.S. feedback on TEPCO's plan.

TEPCO's Katsumata said he was not sure when the tens of thousands who had been forced to flee their homes because of the crisis could go back, but Trade Minister Banri Kaieda said some could return home within six to nine months.

"Of course, some people will be unable to return home, but we will keep everyone informed," he said, adding that the government hoped TEPCO could contain the radiation sooner than the schedule announced Sunday.

The company is focusing on cooling the reactors and spent fuel pools, decontaminating water that has been contaminated by radiation, mitigating the release of radiation into the atmosphere and soil, and measuring and reducing the amount of radiation affecting the evacuation area, he said.

Calls for resignation
As Japan has begun planning for reconstruction and mulling how to pay for it, Kan's political opponents have resumed calls for his resignation after refraining from criticism in the immediate aftermath of the disaster.

Thanking the international community for its support, Kan vowed to rebuild a country "highly resistant to national disasters."

"I pledge that the Japanese government will promptly and thoroughly verify the cause of this incident, as well as share information and the lessons learned with the rest of the world to help prevent such accidents in the future," he said in the commentary, which also appeared in the New York Times and Washington Post.

Government officials fanned out across the affected areas during the weekend seeking to explain evacuation decisions and calm nerves. Chief Cabinet Secretary Yukio Edano met Sunday with the governor of Fukushima, who has vigorously protested the predicament the nuclear crisis poses for his prefecture.

"The safety of residents is our foremost priority," Edano said. "I told the governor that the government will do everything it can to prevent the crisis from worsening."

Explosions, fires and other malfunctions have hindered efforts to repair the stricken plant and stem radiation leaks.

TEPCO Vice President Sakae Muto said Sunday the Unit 2 containment vessel at the plant was leaky and likely to have been damaged, but added that the spent fuel roads in the cooling pool in Unit 4 were confirmed not to have been damaged, which could have greatly complicated containment efforts.

Officials reported late Saturday that levels of radioactivity had again risen sharply in seawater near the plant, signaling the possibility of new leaks. Workers have been spraying massive amounts of water on the overheated reactors. Some of that water, contaminated with radiation, has leaked into the Pacific.

Plant officials said they plugged that leak on April 5 and radiation levels in the sea initially dropped. Authorities have insisted the radioactivity will dissipate and poses no immediate threat to sea creatures or people who might eat them. Most experts agree.

Regardless, plant workers on Saturday began dumping sandbags filled with sand and zeolite, a mineral that absorbs radioactive cesium, into the sea to combat the radiation leaks.

TEPCO said it planned to establish a system for recycling water contaminated by the radiation and removing salt from the seawater that has been used as an emergency cooling measure but that was also corroding the reactors.

This article contains reporting from msnbc.com staff, The Associated Press and Reuters.

Waves pour over a seawall and roar into a seaside village near the mouth of Hei River on March 11 as the tsunami generated by the massive earthquake hits shore.
(Mainichi Newspaper via EPA)
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An aerial photo shows Sendai Airport being inundated by a tsunami on March 11. Later reports said the first wave hit 26 minutes after the quake struck at 2:46 p.m. local time.
(Kyodo News via Reuters)
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A swirling pattern is evident in this aerial photo of the tsunami as it hit a port in Oarai, Ibaraki prefecture on March 11.
(Kyodo News via AP)
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Toya Chiba, a reporter for local newspaper Iwate Tokai Shimbun, is swept away while taking pictures at the mouth of the Owatari River during the tsunami at Kamaishi port, Iwate prefecture. Chiba managed to survive in the rush of water by grabbing a dangling rope and climbing onto a coal heap around 30 feet high after being swept away for about 100 feet, Kyodo News reports.
(Kamaishi Port Office / Kyodo via Reuters)
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A line of residents seeking water snakes across the playground of a school in Sendai, Miyagi prefecture, on March 13, two days after the earthquake.
(Kyodo News via AP)
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An "SOS" signal scrawled on the sports field of a high school beckons potential rescuers on March 13 in the town of Minami Sanriku, Miyagi prefecture.
(Kyodo News via Reuters)
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The body of a victim of the twin disaster lays on the stairs of a destroyed house in Sendai, Miyagi prefecture, on March 13.
(David Guttenfelder / AP)
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Sixty-year-old Hiromitsu Shinkawa waves to members of Japan Maritime Self-Defence Force preparing to rescue him about 9 miles off Fukushima prefecture on March 13. Shinkawa survived by clinging to a piece of roof after the tsunami hit his hometown of Minamisoma.
(Japanese Defense Forces via AFP - Getty Images)
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An explosion at the Fukushima Dai-ichi nuclear power plant sends a plume of smoke skyward on March 14. The blast was believed to have been caused by a buildup of hydrogen inside the reactor building, caused by the partial meltdown of nuclear fuel inside. The plant was crippled after the earthquake cut power to the station and tsunami waves knocked out backup generators.
(NTV / FCT)
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Officers examine a Mitsubishi F-2 fighter jet of the Japanese Air Self-Defense Force on March 14. The warplane was swept by the tsunami into a building at Matsushima base in Higashimatsushima, Iwate prefecture.
(Kyodo News via Reuters)
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Refugees, including 53 people who were rescued from a retirement home during the tsunami, take shelter inside a school gym in the leveled city of Kesennuma, Miyagi prefecture, on March 17.
(David Guttenfelder / AP)
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Members of Japan Self-Defense Force pray over the body of a tsunami victim in Onagawa, Miyagi prefecture, on March 20.
(Shuji Kajiyama / AP)
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Tomoko Yagi looks at two firetrucks that were tossed around like toys in the tsunami in Kamaishi, Iwate prefecture, on March 20.
(Lee Jae-Won / Reuters)
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Manami Kon, 4, uses the Japanese "hiragana" characters she just learned to write a letter to her missing mother in the devastated city of Miyako, Iwate prefecture, on March 22 . "Dear Mommy. I hope you're alive. Are you OK?" read the letter, which took about an hour to write. Also missing were the little girl's father and sister.
(Norikazu Tateishi / The Yomiuri Shimbun via AP)
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Tokyo Electric Power Co. workers collect data in the control room for the Unit 1 and 2 reactors at the crippled Fukushima Dai-ichi nuclear power plant on March 23.
(Nuclear and Industrial Safety Agency via AP)
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An aerial photo taken by an unmanned drone shows the damaged units of the Fukushima Dai-ichi nuclear plant on March 24.
(Air Photo Service via EPA)
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Two residents exchange words as they are reunited two weeks after the earthquake and tsunami in a makeshift public bath set up outside a shelter in Yamamoto, Miyagi prefecture, on March 25.
(Shuji Kajiyama / AP)
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A Japanese funeral parlor worker shovels dirt onto the coffins of victims of the earthquake and tsunami at a mass funeral in Yamamoto, Miyagi prefecture, on March 26.
(David Guttenfelder / AP)
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A lone pine tree stands in a devastated area iof Rikuzentakaka, Iwate prefecture, on March 27. It was the only one among tens of thousands of other pine trees forming "Takata Matsubara," or Takata seaside pine forest, standing after the March 11 tsunami washed away all the others, local media said.
(Kyodo News via AP)
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A woman whose house was washed away loses control of her emotions on March 29 as she talks about the disaster that befell her hometown of Kesennuma, Miyagi prefecture.
(Kuni Takahashi)
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Officials of the Tokyo Electric Power Co., (TEPCO), including Chairman Tsunehisa Katsumata, center, Vice President Takashi Fujimoto, second from left, bow before a news conference at the company's head office in Tokyo on March 30.
(Itsuo Inouye / AP)
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A man rides a bicycle in between the ships that were washed ashore by the March 11 tsunami, on March 30, in Kesennuma, Miyagi prefecture.
(Eugene Hoshiko / AP)
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An elderly woman waves to her grandchildren in Minamisanriku, Miyagi prefecture, on April 3, as authorities began a mass evacuation of approximately 1,100 homeless survivors to shelters elsewhere.
(Jiji Press via AFP - Getty Images)
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Editor's note:
This image contains graphic content that some viewers may find disturbing.